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Common Bile Duct

Medically reviewed by: Stephanie Curreli, MD, PhD
Last Updated: Dec 15, 2016

The common bile duct is formed by the union of the common hepatic and the cystic ducts. It leads to the duodenum, where a sphincter muscle guards its exit. This sphincter normally remains contracted until the bile is needed, so that bile collects in the common bile duct and backs up to the cystic duct. When this happens, the bile flows into the gallbladder and is stored there.